Every army soldier has to, at least in the early stages, do a lot of square-bashing, fitness training, small-arms training, hand-to-hand combat training, etc.
Beyond this, careers diversify. If you join the catering corp, you'll spend a lot of time cooking. In the medical corp, you'll train up to the field equivalent of paramedic level. There are loads of other jobs. The nearest army base to me is an airfield. Most of the guys there are pilots, mechanics, technicians, etc but they've also got pay staff, caterers and most other jobs which you'd find in 'civvy' life.
Some army staff spend a lot of time on ceremonial duties (e.g. the changing of the guard at Buckingham Palace) or working as musicians but they're all fully-trained combat staff.
So, really, asking what people do in the army is a bit like asking what people who aren't in the army do. There are so many different occupations that it would take ages to list them all.
For more information, start here:
http://www.learndirect-advice.co.uk/helpwithyourcareer/j obprofiles/profiles/profile470/ and then follow the links at the bottom of the page.
Chris